Gas turbine engines are used extensively in high performance aircraft and they employ large fans that are positioned at the front of the engine so as to provide greater thrust and to reduce specific fuel consumption. This in turn, provides greater efficiencies and economical performance which is desired in the competitive airline industry. A fan is disposed within a duct and is driven by a shaft that is connected to the turbine and directs air rearwardly through the duct in the form of bypass air. The duct includes a fan casing that circumscribes the fan and the casing is capable of containing debris and minimizing damage to the engine in the event a catastrophic event occurs such as when birds, hailstones, or other debris enter the duct.
Fan casings can also be equipped with specialized blade containment structures that serve to minimize structural damage to the immediate surroundings of the engine in the event a fan blade is released from its hub during engine operation. This is known as a “blade-off” event, which can be catastrophic to an aircraft. Thus, various configurations have been used for such containment structures including various methods of securing the containment structure to a fan casing.
Serviceability of the fan casing has also become a problem in the event a containment structure has been damaged and needs replaced. For example, if debris were to enter a fan casing, and the integrity of an existing containment structure is diminished, then maintenance workers must service the aircraft by taking the aircraft out of service. Once the aircraft is taken out of service, a repair technician then removes the damaged containment structure and then installs a compatible replacement containment structure. These structures are sometimes referred to as a fan track liner.
Traditionally, containment structures would be glued to the interior surface of the fan casing which, when in need of repair, would require a worker to spend substantial resources in removing the old containment structure. For example, the interior surface of the fan case would need to be reconditioned before installing a new containment structure. Sometimes the containment structures have been known to utilize a bonding agent to affix the structure to the fan case track. Such instances require the entire fan casing to be placed within a large oven in order to cure the bonding agent so as to assure proper adhesive of the containment structure to the fan casing. Fan casings reach up to ten feet in diameter, which means large expensive ovens must be used to complete the bonding agent curing process.
Another problem with utilizing traditional containment structures is that they fail to provide a sufficient containment of debris during a blade-off or other catastrophic event. This may be due to the containment structure being too rigid and not demonstrating the proper collapsible deformation characteristics that may be present during predetermined conditions. For example, it would not be desirable to have a fan track liner collapse due to ice impact. By contrast, having a liner that collapses during a blade-off, or other events, so as to minimize damage to the engine and its surroundings, could be helpful to the industry. It may also be helpful to provide a containment structure that has a predetermined collapsing characteristic or profile.
An exemplary embodiment may overcome these problems and provide a containment structure that more fully meets the demands of today's aircraft industry.